Opposed gratings in a waveguide display

ABSTRACT

A waveguide display includes a light source assembly, an output waveguide, and a controller. The light source assembly emits an image light that propagates along an input wave vector. The output waveguide includes a waveguide body with two opposite surfaces. The output waveguide includes a first grating receiving an image light propagating along the input wave vector, a second grating, and a third grating positioned opposite to the second grating and outputting an expanded image light with wave vectors matching the input wave vector. The controller controls the illumination of the light source assembly to form a two-dimensional image.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/406,464, filed Oct. 11, 2016, which is incorporated by reference inits entirety.

BACKGROUND

The disclosure relates generally to near-eye-display systems, and morespecifically to waveguide displays.

Near-eye light field displays project images directly into a user's eye,encompassing both near-eye displays (NEDs) and electronic viewfinders.Conventional near-eye displays (NEDs) generally have a display elementthat generates image light that passes through one or more lenses beforereaching the user's eyes. Additionally, NEDs in virtual reality systemsand/or augmented reality systems are typically required to be compactand light weight, and to provide very large exit pupil for ease of use.However, designing a conventional NED to have a very large exit pupilcan result in rather large lenses, and a relatively bulky and heavy NED.

SUMMARY

A waveguide display is used for presenting media to a user. In someembodiments, the waveguide display is incorporated into, e.g., anear-eye-display (NED) as part of a virtual reality (VR), augmentedreality (AR), mixed reality (MR), or some combination thereof, system.The waveguide display includes a light source, a controller, and anoutput waveguide. The light source emits image light in accordance withdisplay instructions generated and provided by the controller. The lightsource emits image light that is at least partially coherent andpropagates along an input wave vector. The controller controls theillumination of the light source to form a two-dimensional image. Lightfrom the light source is in-coupled into the output waveguide through anin-coupling area located at one end of the output waveguide. The outputwaveguide outputs the image light at a location offset from the entrancelocation, and the location/direction of the emitted image light is basedin part on the orientation of the light source.

The output waveguide includes a waveguide body with two oppositesurfaces. The output waveguide includes a first grating (e.g., an inputgrating) on at least one of the opposite surfaces. The first gratingin-couples the image light (propagating along an input wave vector)emitted from the light source into the output waveguide, and the firstgrating has an associated first grating vector. The output waveguideexpands the image light in two dimensions. The output waveguide includesa second and third grating (e.g., an output grating) that are associatedwith a second and third grating vector, respectively that togetherdirect and decouple the expanded image light from the output waveguide,the output expanded image light having a wave vector that matches theinput wave vector. The first grating, the second grating, and the thirdgrating are designed such that the vector sum of all their associatedgrating vectors is less than a threshold value, and the threshold valueis close to or equal to zero. In some embodiments, the waveguide displayincludes multiple waveguides that are stacked together to output anexpanded image light projected along multiple planes as a polychromaticdisplay to the user's eyes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a NED, in accordance with an embodiment.

FIG. 2 is a cross-section of the NED illustrated in FIG. 1, inaccordance with an embodiment.

FIG. 3 illustrates an isometric view of a waveguide display, inaccordance with an embodiment.

FIG. 4 illustrates a cross-section of the waveguide display shown inFIG. 3, in accordance with an embodiment.

FIG. 5 illustrates a cross-section of a waveguide display that includesan output waveguide including four gratings, in accordance with anembodiment.

FIG. 6A illustrates an example path of a wave vector in an equilateralconfiguration, according to an embodiment.

FIG. 6B illustrates an example path of a wave vector in anon-equilateral configuration, according to an embodiment.

FIG. 6C illustrates an example path of a wave vector in a parallelogramconfiguration, in accordance with an embodiment.

FIG. 6D illustrates an example path of a wave vector in a triangularconfiguration, in accordance with an embodiment.

FIG. 6E illustrates an example path of a wave vector in a triangularconfiguration with two sets of decoupling elements, in accordance withan embodiment.

FIG. 7 is a block diagram of a system including the NED of FIG. 1, inaccordance with an embodiment.

The figures depict embodiments of the present disclosure for purposes ofillustration only. One skilled in the art will readily recognize fromthe following description that alternative embodiments of the structuresand methods illustrated herein may be employed without departing fromthe principles, or benefits touted, of the disclosure described herein.

DETAILED DESCRIPTION

A waveguide display is used for presenting media to a user. In someembodiments, the waveguide display is incorporated into, e.g., anear-eye-display (NED) as part of a virtual reality (VR), augmentedreality (AR), mixed reality (MR), or some combination thereof, system.The waveguide display includes a source assembly, a controller, and anoutput waveguide. The source assembly includes a source and an opticssystem. The source assembly projects a line image to an infinite viewingdistance through a small exit pupil. The line image can be formed by,for example, using a linear array of sources and a collimating lens. Thecontroller controls the illumination of the source to form atwo-dimensional image. Light from the source is in-coupled into theoutput waveguide through an in-coupling area located at one end of theoutput waveguide. The output waveguide outputs the image light at alocation offset from the entrance location, and the location/directionof the emitted image light is based in part on the orientation of thesource assembly. The output waveguide includes a waveguide body with twoopposite surfaces. The output waveguide includes an input diffractiongrating on at least one of the opposite surfaces. The input diffractiongrating in-couples the image light (propagating along an input wavevector) emitted from the source assembly into the output waveguide, andthe input diffraction grating has an associated first grating vector. Awave vector of a plane wave is a vector which points in the direction inwhich the wave propagates (perpendicular to the wavefront associatedwith an image light) and its magnitude is inversely proportional to thewavelength of the light. In some configurations, the wave vector (k_(r))is defined to be 2π/λ, where λ, is the wavelength of the light. Forexample, a light for a projector is associated with a radial wave vector(k_(r0)) which has a magnitude of zero for a normal incidence on asurface of the output waveguide. In this disclosure, only the radialcomponent of the wave vector (parallel to the waveguide surface) isused. Radial component does not change as the light enters or exits themedium (e.g. waveguide). A grating vector is a vector whose direction isnormal to the grating grooves and its vector size is inverselyproportional to its pitch. In some configurations, the grating vector(k_(grating)) is defined to be 2π/p, where p is the pitch of thegrating. Since grating is on the waveguide surface, the grating vectoris always parallel to the surface, and thus it affects only the radialcomponent of the wave vector of the image light. Accordingly, the radialcomponent of the wave vector (k_(r)) of an image light bouncing back andforth in the output waveguide is changed to k_(r)=k_(r0)+Σk_(grating),where Σk_(grating) is a vector sum of the grating vectors associatedwith the gratings in a waveguide.

The output waveguide expands the image light in two dimensions. Theoutput waveguide includes a second and third grating (that areassociated with a second and third grating vector, respectively) thattogether direct and decouple the expanded image light from the outputwaveguide, the output expanded image light having a wave vector thatmatches the input wave vector. The input diffraction grating, the seconddiffraction grating, and the third diffraction grating are designed suchthat the vector sum of all their associated grating vectors is less thana threshold value, and the threshold value is close to or equal to zero.

The orientation of the light source is determined by the controllerbased on the display instructions provided to the light source. Notethat the image light used in the waveguide display is polychromatic foreach of the primary colors (red, green, and blue) with a finitebandwidth of wavelength. The display acts as a two-dimensional imageprojector with an extended pupil over two orthogonal dimensions. In someembodiments, the waveguide display includes multiple output waveguidesthat are stacked together to output an expanded image light that isfull-colored. In alternate embodiments, the waveguide display includesmultiple waveguides that are stacked together to output an expandedimage light projected along multiple planes as monochromatic orpolychromatic display to the user's eyes.

FIG. 1 is a diagram of a near-eye-display (NED) 100, in accordance withan embodiment. The NED 100 presents media to a user. Examples of mediapresented by the NED 100 include one or more images, video, audio, orsome combination thereof. In some embodiments, audio is presented via anexternal device (e.g., speakers and/or headphones) that receives audioinformation from the NED 100, a console (not shown), or both, andpresents audio data based on the audio information. The NED 100 isgenerally configured to operate as a VR NED. However, in someembodiments, the NED 100 may be modified to also operate as an augmentedreality (AR) NED, a mixed reality (MR) NED, or some combination thereof.For example, in some embodiments, the NED 100 may augment views of aphysical, real-world environment with computer-generated elements (e.g.,images, video, sound, etc.).

The NED 100 shown in FIG. 1 includes a frame 105 and a display 110. Theframe 105 is coupled to one or more optical elements which togetherdisplay media to users. In some embodiments, the frame 105 may representa frame of eye-wear glasses. The display 110 is configured for users tosee the content presented by the NED 100. As discussed below inconjunction with FIG. 2, the display 110 includes at least one waveguidedisplay assembly (not shown) for directing one or more image light to aneye of the user. The waveguide display assembly includes, e.g., awaveguide display, a stacked waveguide display, a varifocal waveguidedisplay, or some combination thereof. The stacked waveguide display is apolychromatic display created by stacking waveguide displays whoserespective monochromatic sources are of different colors. The stackedwaveguide display is also a polychromatic display that can be projectedon multiple planes (e.g. multi-planar display). The varifocal waveguidedisplay is a display that can adjust a focal position of image lightemitted from the waveguide display.

FIG. 2 is a cross-section 200 of the NED 100 illustrated in FIG. 1, inaccordance with an embodiment. The display 110 includes at least onedisplay assembly 210. An exit pupil 230 is a location where the eye 220is positioned when the user wears the NED 100. For purposes ofillustration, FIG. 2 shows the cross section 200 associated with asingle eye 220 and a single display assembly 210, but in alternativeembodiments not shown, another waveguide display assembly which isseparate from the waveguide display assembly 210 shown in FIG. 2,provides image light to another eye 220 of the user.

The display assembly 210, as illustrated below in FIG. 2, is configuredto direct the image light to the eye 220 through the exit pupil 230. Thedisplay assembly 210 may be composed of one or more materials (e.g.,plastic, glass, etc.) with one or more refractive indices thateffectively minimize the weight and widen a field of view (hereinafterabbreviated as ‘FOV’) of the NED 100. In alternate configurations, theNED 100 includes one or more optical elements between the displayassembly 210 and the eye 220. The optical elements may act to, e.g.,correct aberrations in image light emitted from the display assembly210, magnify image light emitted from the display assembly 210, someother optical adjustment of image light emitted from the displayassembly 210, or some combination thereof. The example for opticalelements may include an aperture, a Fresnel lens, a convex lens, aconcave lens, a filter, or any other suitable optical element thataffects image light.

In some embodiments, the display assembly 210 includes a stack of one ormore waveguide displays including, but not restricted to, a stackedwaveguide display, a varifocal waveguide display, etc. The stackedwaveguide display is a polychromatic display (e.g., a red-green-blue(RGB) display) created by stacking waveguide displays whose respectivemonochromatic sources are of different colors. The stacked waveguidedisplay is also a polychromatic display that can be projected onmultiple planes (e.g. multi-planar colored display). In someconfigurations, the stacked waveguide display is a monochromatic displaythat can be projected on multiple planes (e.g. multi-planarmonochromatic display). The varifocal waveguide display is a displaythat can adjust a focal position of image light emitted from thewaveguide display. In alternate embodiments, the display assembly 210may include the stacked waveguide display and the varifocal waveguidedisplay.

FIG. 3 illustrates an isometric view of a waveguide display 300, inaccordance with an embodiment. In some embodiments, the waveguidedisplay 300 is a component (e.g., display assembly 210) of the NED 100.In alternate embodiments, the waveguide display 300 is part of someother NED, or other system that directs display image light to aparticular location.

The waveguide display 300 includes at least a source assembly 310, anoutput waveguide 320, and a controller 330. For purposes ofillustration, FIG. 3 shows the waveguide display 300 associated with asingle eye 220, but in some embodiments, another waveguide displayseparate (or partially separate) from the waveguide display 300,provides image light to another eye of the user. In a partially separatesystem, one or more components may be shared between waveguide displaysfor each eye.

The source assembly 310 generates image light. The source assembly 310includes an optical source, and an optics system (e.g., as furtherdescribed below with regard to FIG. 4). The source assembly 310generates and outputs image light 355 to a coupling element 350 locatedon a first side 370 of the output waveguide 320. The image light 355propagates along a dimension with an input wave vector as describedbelow with reference to FIG. 6.

The output waveguide 320 is an optical waveguide that outputs imagelight to an eye 220 of a user. The output waveguide 320 receives theimage light 355 at one or more coupling elements 350 located on thefirst side 370, and guides the received input image light to decouplingelement 360A. In some embodiments, the coupling element 350 couples theimage light 355 from the source assembly 310 into the output waveguide320. The coupling element 350 may be, e.g., a diffraction grating, aholographic grating, one or more cascaded reflectors, one or moreprismatic surface elements, an array of holographic reflectors, or somecombination thereof. In some configurations, each of the couplingelements 350 have substantially the same area along the X-axis and theY-axis dimension, and are separated by a distance along the Z-axis (e.g.on the first side 370 and the second side 380, or both on the first side370 but separated with an interfacial layer (not shown), or on thesecond side 380 and separated with an interfacial layer or both embeddedinto the waveguide body of the output waveguide 320 but separated withthe interface layer). The coupling element 350 has a first gratingvector. The pitch of the coupling element 350 may be 300-600 nm.

The decoupling element 360A redirects the total internally reflectedimage light from the output waveguide 320 such that it may be decoupledvia the decoupling element 360B. The decoupling element 360A is part of,or affixed to, the first side 370 of the output waveguide 320. Thedecoupling element 360B is part of, or affixed to, the second side 380of the output waveguide 320, such that the decoupling element 360A isopposed to the decoupling element 360B. Opposed elements are opposite toeach other on a waveguide. In some configurations, there may be anoffset between the opposed elements. For example, the offset can be onequarter of the length of an opposed element. The decoupling elements360A and 360B may be, e.g., a diffraction grating, or a holographicgrating, one or more cascaded reflectors, one or more prismatic surfaceelements, an array of holographic reflectors, or some combinationthereof. In some configurations, each of the decoupling elements 360Ahave substantially the same area along the X-axis and the Y-axisdimension, and are separated by a distance along the Z-axis (e.g. on thefirst side 370 and the second side 380, or both on the first side 370but separated with an interfacial layer (not shown), or on the secondside 380 and separated with an interfacial layer or both embedded intothe waveguide body of the output waveguide 320 but separated with theinterface layer). The decoupling element 360A has an associated secondgrating vector, and the decoupling element 360B has an associated thirdgrating vector. An orientation and position of the image light exitingfrom the output waveguide 320 is controlled by changing an orientationand position of the image light 355 entering the coupling element 350.The pitch of the decoupling element 360A and/or the decoupling element360B may be 300-600 nm. In some configurations, the decoupling element360A receives an image light from the coupling element 350 covering afirst portion of the first angular range emitted by the source assembly310, the decoupling element 360B diffracts the image light to a firstorder of diffraction in order to trap the image light in the outputwaveguide 320. In alternate configurations, the decoupling element 360Breceives the image light from the coupling element 350 covering a secondportion of the first angular range emitted by the source assembly 310,and the decoupling element 360A diffracts the image light to a firstdiffracted order in order to trap the image light in the outputwaveguide 320.

The coupling element 350, the decoupling element 360A, and thedecoupling element 360B are designed such that a sum of their respectivegrating vectors is less than a threshold value, and the threshold valueis close to or equal to zero. Accordingly, the image light 355 enteringthe output waveguide 320 is propagating in the same direction when it isoutput as image light 340 from the output waveguide 320. Moreover, inalternate embodiments, additional coupling elements and/or de-couplingelements may be added. And so long as the sum of their respectivegrating vectors is less than the threshold value, the image light 355and the image light 340 propagate in the same direction. The location ofthe coupling element 350 relative to the decoupling element 360A and thedecoupling element 360B as shown in FIG. 3 is only an example. In otherconfigurations, the location could be on any other portion of the outputwaveguide 320 (e.g. a top edge of the first side 370, a bottom edge ofthe first side 370). In some embodiments, the waveguide display 300includes a plurality of source assemblies 310 and/or a plurality ofcoupling elements 350 to increase the FOV further.

The output waveguide 320 includes a waveguide body with the first side370 and a second side 380 that are opposite to each other. In theexample of FIG. 3, the waveguide body includes the two oppositesides—the first side 370 and the second side 380, each of the oppositesides representing a plane along the X-dimension and Y-dimension. Theoutput waveguide 320 may be composed of one or more materials thatfacilitate total internal reflection of the image light 355. The outputwaveguide 320 may be composed of e.g., silicon, plastic, glass, orpolymers, or some combination thereof. The output waveguide 320 has arelatively small form factor. For example, the output waveguide 320 maybe approximately 50 mm wide along X-dimension, 30 mm long alongY-dimension and 0.5-1 mm thick along Z-dimension.

The controller 330 controls the illumination operations of the sourceassembly 310. The controller 330 determines display instructions for thesource assembly 310. Display instructions are instructions to render oneor more images. In some embodiments, display instructions may simply bean image file (e.g., bitmap). The display instructions may be receivedfrom, e.g., a console of a system (e.g., as described below inconjunction with FIG. 7). Display instructions are instructions used bythe source assembly 310 to generate image light 340. The displayinstructions may include, e.g., a type of a source of image light (e.g.monochromatic, polychromatic), one or more illumination parameters(described below with reference to FIG. 4), or some combination thereof.The controller 330 includes a combination of hardware, software, and/orfirmware not shown here so as not to obscure other aspects of thedisclosure.

In alternate configurations (not shown), the output waveguide 320includes the coupling element 350 on the first side 370 and a secondcoupling element (not shown here) on the second side 380. The couplingelement 350 receives an image light 355 from the source assembly 310.The coupling element on the second side 380 receives an image light fromthe source assembly 310 and/or a different source assembly. Thecontroller 330 determines the display instructions for the sourceassembly 310 based at least on the one or more display instructions.

In alternate configurations, the output waveguide 320 may be orientedsuch that the source assembly 310 generates the image light 355propagating along an input wave vector in the Z-dimension. The outputwaveguide 320 outputs the image light 340 propagating along an outputwave vector that matches the input wave vector. In some configurations,the image light 340 is a monochromatic image light that can be projectedon multiple planes (e.g. multi-planar monochromatic display). Inalternate configurations, the image light 340 is a polychromatic imagelight that can be projected on multiple planes (e.g. multi-planarpolychromatic display).

In some embodiments, the output waveguide 320 outputs the expanded imagelight 340 to the user's eye 220 with a very large FOV. For example, theexpanded image light 340 couples to the user's eye 220 with a diagonalFOV (in x and y) of at least 60 degrees. Generally, the horizontal FOVis larger than the vertical FOV. If the aspect ratio is 16:9, theproduct of the horizontal FOV and the vertical FOV will be ˜52×30degrees whose diagonal FOV is 60 degrees for instance.

FIG. 4 illustrates a cross-section of the waveguide display 300 shown inFIG. 3, in accordance with an embodiment. The cross-section 400 of thewaveguide display 300 includes at least the source assembly 310 and theoutput waveguide 320.

The source assembly 310 generates light in accordance with displayinstructions from the controller 330. The source assembly 310 includes asource 410, and an optics system 420. The source 410 is a source oflight that generates at least a coherent or partially coherent imagelight. The source 410 may be, e.g., laser diode, a vertical cavitysurface emitting laser, a light emitting diode, a tunable laser, aMicroLED, a superluminous LED (SLED), or some other light source thatemits coherent or partially coherent light. The source 410 emits lightin a visible band (e.g., from about 390 nm to 700 nm), and it may emitlight that is continuous or pulsed. In some embodiments, the source 410may be a laser that emits light at a particular wavelength (e.g., 532nanometers). The source 410 emits light in accordance with one or moreillumination parameters received from the controller 330. Anillumination parameter is an instruction used by the source 410 togenerate light. An illumination parameter may include, e.g., restrictionof input wave vector for total internal reflection, restriction of inputwave vector for maximum angle, source wavelength, pulse rate, pulseamplitude, beam type (continuous or pulsed), other parameter(s) thataffect the emitted light, or some combination thereof.

The optics system 420 includes one or more optical components thatcondition the light from the source 410. Conditioning light from thesource 410 may include, e.g., expanding, collimating, adjustingorientation in accordance with instructions from the controller 330,some other adjustment of the light, or some combination thereof. The oneor more optical components may include, e.g., lenses, mirrors,apertures, gratings, or some combination thereof. In someconfigurations, the optics system 420 includes liquid lens with aplurality of electrodes that allows scanning a beam of light with athreshold value of scanning angle in order to shift the beam of light toa region outside the liquid lens. In an alternate configuration, theoptics system 420 includes a voice coil motor that performs a onedimensional scanning of the light to a threshold value of scanningangle. The voice coil motor performs a movement of one or more lens tochange a direction of the light outside the one or more lens in order tofill in the gaps between each of the multiple lines scanned. Lightemitted from the optics system 420 (and also the source assembly 310) isreferred to as image light 355. The optics system 420 outputs the imagelight 355 at a particular orientation (in accordance with the displayinstructions) toward the output waveguide 320. The image light 355propagates along an input wave vector such that the restrictions forboth total internal reflection and maximum angle of propagation are met.

The output waveguide 320 receives the image light 355. The couplingelement 350 at the first side 370 couples the image light 355 from thesource assembly 310 into the output waveguide 320. In embodiments wherethe coupling element 350 is diffraction grating, the pitch of thediffraction grating is chosen such that total internal reflectionoccurs, and the image light 355 propagates internally toward thedecoupling element 360A. For example, the pitch of the coupling element350 may be in the range of 300 nm to 600 nm. In alternate embodiments,the coupling element 350 is located at the second side 380 of the outputwaveguide 320.

The decoupling element 360A redirects the image light 355 toward thedecoupling element 360B for decoupling from the output waveguide 320. Inembodiments where the decoupling element 360A is a diffraction grating,the pitch of the diffraction grating is chosen to cause incident imagelight 355 to exit the output waveguide 320 at a specific angle ofinclination to the surface of the output waveguide 320. An orientationof the image light exiting from the output waveguide 320 may be alteredby varying the orientation of the image light exiting the sourceassembly 310, varying an orientation of the source assembly 310, or somecombination thereof. For example, the pitch of the diffraction gratingmay be in the range of 300 nm to 600 nm. Both the coupling element 350and the decoupling element 360A are designed such that a sum of theirrespective grating vectors is less than a threshold value, and thethreshold value is close to or equal to zero.

In some configurations, the first decoupling element 360A receives theimage light 355 from the coupling element 350 after total internalreflection in the waveguide body and transmits an expanded image lightto the second decoupling element 360B at the second side 380. The seconddecoupling element 360B decouples the expanded image light 340 from thesecond side 380 of the output waveguide 320 to the user's eye 220. Thefirst decoupling element 360A and the second decoupling element 360B arestructurally similar. In alternate configurations, the second decouplingelement 360B receives the image light 355 after total internalreflection in the waveguide body and transmits an expanded image lightfrom the first decoupling element 360A on the first side 370.

The image light 340 exiting the output waveguide 320 is expanded atleast along one dimension (e.g., may be elongated along X-dimension).The image light 340 couples to the human eye 220. The image light 340exits the output waveguide 320 such that a sum of the respective gratingvectors of each of the coupling element 350, the decoupling element360A, and the decoupling element 360B is less than a threshold value,and the threshold value is close to or equal to zero. An exact thresholdvalue is going to be system specific, however, it should be small enoughto not degrade image resolution beyond acceptable standards (if non-zerodispersion occurs and resolution starts to drop). In someconfigurations, the image light 340 propagates along wave vectors alongat least one of X-dimension, Y-dimension, and Z-dimension.

In alternate embodiments, the image light 340 exits the output waveguide320 via the decoupling element 360A. Note the decoupling elements 360Aand 360B are larger than the coupling element 350, as the image light340 is provided to an eyebox located at an exit pupil of the waveguidedisplay 300.

In another embodiment, the waveguide display 300 includes two or moredecoupling elements. For example, the decoupling element 360A mayinclude multiple decoupling elements located side by side with anoffset. In another example, the decoupling element 360A may includemultiple decoupling elements stacked together to create atwo-dimensional decoupling element.

The controller 330 controls the source assembly 310 by providing displayinstructions to the source assembly 310. The display instructions causethe source assembly 310 to render light such that image light exitingthe decoupling element 360A of the output waveguide 320 scans out one ormore 2D images. For example, the display instructions may cause thesource assembly 310 (via adjustments to optical elements in the opticssystem 420) to scan out an image in accordance with a scan pattern(e.g., raster, interlaced, etc.). The display instructions control anintensity of light emitted from the source 410, and the optics system420 scans out the image by rapidly adjusting orientation of the emittedlight. If done fast enough, a human eye integrates the scanned patterninto a single 2D image.

Stacked Waveguide Display

A collimated beam of image light has one or more physical properties,including, but not restricted to, wavelength, luminous intensity, flux,etc. The wavelength of collimated beam of image light from a sourceassembly (e.g., 410) strongly impacts, among several other parameters,the FOV, as described above in conjunction with FIG. 2, of the NED 100.The FOV would be very small in cases where a source assembly emits imagelight across an entire visible band of image light. However, thewaveguide display 300 has a relatively large FOV as the waveguidedisplay 300 includes a mono-chromatic source in the example shown inFIG. 4. Accordingly, to generate a polychromatic display that has alarge FOV, one or more monochromatic waveguide displays (with one ormore image light at different wavelengths) are stacked to generate asingle polychromatic stacked waveguide display.

The waveguide display 400 of FIG. 4 shows an example with a singleoutput waveguide 320 receiving a monochromatic beam of image light 355from the source assembly 310. In alternate embodiments, the waveguidedisplay 400 includes a plurality of source assemblies 310 and aplurality of output waveguides 320. Each of the source assemblies 310emits a monochromatic image light of a specific band of wavelengthcorresponding to one of the primary colors (red, green, and blue). Eachof the output waveguides 320 may be stacked together with a distance ofseparation to output an expanded image light 340 that is multi-colored.The output waveguides are stacked such that image light (e.g., 340) fromeach of the stacked waveguides occupies a same area of the exit pupil ofthe stacked waveguide display. For example, the output waveguides may bestacked such that decoupling elements from adjacent optical waveguidesare lined up and light from a rear output waveguide would pass throughthe decoupling element of the waveguide adjacent to and in front of theread output waveguide. In some configurations, the expanded image light340 can couple to the user's eye 220 as a multi-planar display. Forexample, the expanded image light 340 may include a display along atleast two of the X-Y plane, Y-Z plane, and the X-Z plane.

In alternate embodiments, the location of the coupling element 350 canbe located on the second side 380. In some configurations, the waveguidedisplay 400 may perform an illumination operation of the source 410inside the source assembly 310 to form a line image. The location of thecoupling element 350 shown in FIG. 4 is only an example, and severalother arrangements are apparent to one of ordinary skill in the art.

FIG. 5 illustrates a cross-section of a waveguide display 500 thatincludes the output waveguide 320 including four gratings, in accordancewith an embodiment. The waveguide display 500 is an embodiment of thewaveguide display 300. The waveguide display 500 is substantiallysimilar to the waveguide display 300 except that it also includes acoupling element 550, and that the grating vectors for one or more ofthe coupling elements and decoupling elements may be different fromthose described above with respect to FIGS. 3 and 4.

The output waveguide 320 includes the first coupling element 350, asecond coupling element 550, the decoupling element 360A, and thedecoupling element 360B. The coupling element 550 is an embodiment ofthe coupling element 350 of FIG. 4. The coupling element 550 may be,e.g., a diffraction grating, a holographic grating, some other elementthat couples the image light 355 into the output waveguide 320, or somecombination thereof. The coupling element 550 increases the couplingefficiency of the waveguide display across a large FOV. In someembodiments, the FOV is divided into a first and second portion, and thecoupling element 350 diffracts a first portion of the FOV and thecoupling element 550 diffracts the second portion the FOV. Accordingly,the entire FOV can be covered by the coupling element 350, the couplingelement 550, or both.

In the example of FIG. 5, the output waveguide 320 includes the firstcoupling element 350 at the first side 370 that is away from the user'seye 220. The output waveguide 320 includes the second coupling element550 at the second side 380 that is closer to the user's eye 220. Theoutput waveguide 320 receives the image light 355 emitted from thesource assembly 310 at the coupling element 350. The image light 355propagates along a wave vector in the Z-dimension. The coupling element350 couples the image light 355 from the source assembly 310 into theoutput waveguide 320. The decoupling element 360A redirects the imagelight in accordance with its grating vector. The decoupling element 360Bdecouples the image light 340 from the output waveguide 320 such that asum of the respective grating vectors of each of the coupling element350, the decoupling element 360A, and the decoupling element 360B isless than a threshold value, and the threshold value is close to orequal to zero. In some examples, the possible orders of summation ofgrating vectors may include: (1) an input grating vector associated withthe coupling element 350, a grating vector associated with thedecoupling element 360A, and a grating vector associated with thedecoupling element 360B, (2) the input grating vector associated withthe coupling element 350, the grating vector associated with thedecoupling element 360B, and the grating vector associated with thedecoupling element 360A, (3) a second input grating vector associatedwith the coupling element 550, the grating vector associated with thedecoupling element 360A, and the grating vector associated with thedecoupling element 360B, and (4) the second input grating vectorassociated with the coupling element 550, the grating vector associatedwith the decoupling element 360B, and the grating vector associated withthe decoupling element 360A. In an alternate embodiment (not shown), theoutput waveguide 320 receives the image light 355 emitted from thesource assembly 310 at the coupling element 550 which is located at thesecond side 380.

In a different configuration, the cross-section of the waveguide display500 includes the source assembly 310 and/or different source assemblies.The controller 330 provides display instructions to each of the sourceassemblies 310 to render image light exiting the decoupling element 360Bof the output waveguide 320 that scans out one or more 2D images suchthat a sum of the respective grating vectors of each of the couplingelement 350, the decoupling element 360A, and the decoupling element360B is less than a threshold value, and the threshold value is close toor equal to zero.

The design of the diffraction grating used in the coupling element 350,and the coupling element 550 are such that the conditions for both therestriction on the occurrence of total internal reflection and a maximumangle (θ_(max)) restriction are satisfied. In some configurations, therestriction on the radial wave vector is governed by the physicalrelationship shown by the inequality below:2π/λ₀ ≤|k _(r)|≤2πn sin(θ_(max))/λ₀  (1)where |k_(r)| is the magnitude of the radial wave vector n is therefractive index of the output waveguide 320, and λ₀ is the centerwavelength of the image light 355. The lower limit of the inequality (1)above restricts the condition on total internal reflection of the imagelight 355 and the upper limit restricts the condition on the maximumangle. The threshold value on the maximum angle is based on a desiredlevel of the light bouncing back and forth in the waveguide. In someexamples, the maximum angle (θ_(max)) can be at most 75 degrees and therefractive index (n) can be in the range of 1.5-1.9

FIG. 6A illustrates an example path 600 of wave vector in an equilateralconfiguration, according to an embodiment. The example path 600 is apath of a wave vector of the image light that is affected by the gratingvectors of the coupling element and the decoupling elements that theimage light meets. In the example path 600, image light from the sourceassembly is associated with a projected radial wave vector, k_(r0) 610.The image light is coupled into the output waveguide via a couplingelement associated with an input grating vector, k_(couple) 620. Thein-coupled light is then diffracted by a first decoupling elementassociated with a grating vector, k_(decouple1) 630. The light is thendiffracted (and out coupled from the output waveguide) by a seconddecoupling element associated with a grating vector, k_(decouple2) 640.Note that the summation of the k_(couple) 620, the k_(decouple1) 630,and the k_(decouple2) 640 is zero (i.e., grating vectors return to point615). Additionally, there are other embodiments of grating vectors thatresult in a zero summation. For example, the k_(couple) 620, ak_(decouple2) 642, and a k_(decouple1) 632.

The magnitude of the radial wave vector (k_(r)) of the light should beless than a radius of an outer circle 655 in order to remain coupled inthe output waveguide and also more than the condition for the occurrenceof total internal reflection. The radius of the outer circle 655 is afunction of the refractive index of the output waveguide, the maximumangle (θ_(max)), and the center wavelength of the image light as shownin the inequality (1) above. Accordingly, to meet these conditions, theradial wave vector (k_(r)) of the light should be in a shaded portion660. For example, k_(r1) (=k_(r0)+k_(couple)) is within the shadedportion 660, so the incoupling was successful in the figure.

The coupling element, the first decoupling element, and the seconddecoupling element, are diffraction gratings whose grating vectors sumto a value that is less than a threshold value, and the threshold valueis close to or equal to zero. In this example, a zero summation occurs,as the vector path returns to its origination point 615. With theoccurrence of the zero summation, the image light exits the outputwaveguide with the same angle as the incident angle from the sourceassembly since the remaining radial wave vector is the k_(r0) 610associated with the FOV of the waveguide display.

Note this is a very simple example, and there are many alternativeembodiments, as described below in conjunction with FIG. 6B-D, includingvarious diffraction gratings whose summation of grating vectors returnsto the origination point 615. For example, the path 600 is shaped likean equilateral triangle with an equal magnitude of the k_(couple) 620,the k_(decouple1) 630 and the k_(decouple2) 640, other paths may be ahexagon, a pentagon, a parallelogram, a rectangle, or any other shapewhose sum of grid vectors is less than the threshold value.

FIG. 6B illustrates an example path 602 of a wave vector in anon-equilateral configuration, according to an embodiment. The examplepath 602 is associated with a coupling element and decoupling elements.The example path 602 of FIG. 6B is an embodiment of the example 600 ofFIG. 6A except that the magnitudes of at least two of k_(couple) 622,k_(decouple1) 634, and k_(decouple2) 644 or k_(couple) 622,k_(decouple1) 636, and k_(decouple2) 646 are not equal. Again note thatthe vector sum of the grating vectors is zero.

FIG. 6C illustrates an example path 604 of a wave vector in aparallelogram configuration, in accordance with an embodiment. Theexample path 604 is associated with a coupling element, and twodifferent decoupling elements. The design of the k_(decouple1) 672 issuch that its direction and magnitude results in a zero summation at asummation point 625. In the example path 604, the possible order ofsummation also includes the k_(couple) 624, the k_(decouple1) 674, thek_(decouple2) 682, and a k_(decouple1) 670, or the k_(couple) 624, thek_(decouple1) 638, the k_(decouple2) 648, and a k_(decouple1) 672. Theexample path 604 illustrates the scenario when the image light isreflected by the decoupling elements three times. Note that the vectorsum of the grating vectors is zero.

FIG. 6D illustrates an example path 606 of a wave vector in a triangularconfiguration, in accordance with an embodiment. The example path 606 isassociated with a coupling element and three decoupling elements. Forthe path 606, two of the three decoupling elements are on the same sideof the output waveguide. In the example path 606, the possible order ofsummation can be k_(couple) 626, a k_(decouple2) 684, and ak_(decouple3) 652, or k_(couple) 626, a k_(decouple2) 676, and ak_(decouple3) 653. Note that the two decoupling elements on the sameside are associated with k_(decouple1) 676 and k_(decouple2) 684. Notethat the vector sum of the grating vectors is zero.

FIG. 6E illustrates an example path of a wave vector in a triangularconfiguration with two sets of decoupling elements, in accordance withan embodiment. The example path 608 is associated with a couplingelement, and a first set of decoupling elements. The example path 610 isassociated with the coupling element, and a second set of decouplingelements. The first set of decoupling elements and the second set ofdecoupling elements together include five different decoupling elements.The design of the k_(decouple0) 686 is such that its direction andmagnitude results in a zero summation at a summation point 690. In theexample path 608, the possible order of summation includes thek_(couple) 628, the k_(decouple1) 688, the k_(decouple2) 676, and thek_(decouple0) 686. In the example path 610, the possible order ofsummation includes the k_(couple) 628, the k_(decouple3) 692, thek_(decouple4) 694, and the k_(decouple0) 686. The example path 608 andthe example path 610 illustrate the scenario when the image light isreflected by the decoupling elements three times. Note that the vectorsum of the grating vectors is zero.

FIG. 7 is a block diagram of a system 700 including the NED 100,according to an embodiment. The system 700 shown by FIG. 7 comprises theNED 100, an imaging device 735, and an input/output interface 740 thatare each coupled to the console 710. While FIG. 7 shows an examplesystem 700 including one NED 100, one imaging device 735, and oneinput/output interface 740, in other embodiments, any number of thesecomponents may be included in the system 700. For example, there may bemultiple NEDs 100 each having an associated input/output interface 740and being monitored by one or more imaging devices 735, with each NED100, input/output interface 740, and imaging devices 735 communicatingwith the console 710. In alternative configurations, different and/oradditional components may be included in the system 700. Similarly,functionality of one or more of the components can be distributed amongthe components in a different manner than is described here. Forexample, some or all of the functionality of the console 710 may becontained within the NED 100. Additionally, in some embodiments thesystem 700 may be modified to include other system environments, such asan AR system environment and/or a mixed reality (MR) environment.

The NED 100 is a near-eye display that presents media to a user.Examples of media presented by the NED 100 include one or more images,video, audio, or some combination thereof. In some embodiments, audio ispresented via an external device (e.g., speakers and/or headphones) thatreceives audio information from the NED 100, the console 710, or both,and presents audio data based on the audio information. In someembodiments, the NED 100 may also act as an AR eye-wear glass. In theseembodiments, the NED 100 augments views of a physical, real-worldenvironment with computer-generated elements (e.g., images, video,sound, etc.).

The NED 100 includes a waveguide display assembly 715, one or moreposition sensors 725, and the inertial measurement unit (IMU) 730. Thewaveguide display assembly 715 includes at least the source assembly310, output waveguide 320, and the controller 330. The output waveguide320 includes multiple diffraction gratings such that light entering theoutput waveguide 320 exits the waveguide display assembly 715 at thesame angle. Details for various embodiments of the waveguide displayelement are discussed in detail with reference to FIGS. 3 and 4. Thewaveguide display assembly includes, e.g., a waveguide display, astacked waveguide display, a varifocal waveguide display, or somecombination thereof.

The IMU 730 is an electronic device that generates fast calibration dataindicating an estimated position of the NED 100 relative to an initialposition of the NED 100 based on measurement signals received from oneor more of the position sensors 725. A position sensor 725 generates oneor more measurement signals in response to motion of the NED 100.Examples of position sensors 725 include: one or more accelerometers,one or more gyroscopes, one or more magnetometers, another suitable typeof sensor that detects motion, a type of sensor used for errorcorrection of the IMU 730, or some combination thereof. The positionsensors 725 may be located external to the IMU 730, internal to the IMU730, or some combination thereof. In the embodiment shown by FIG. 7, theposition sensors 725 are located within the IMU 730, and neither the IMU730 nor the position sensors 725 are visible to the user (e.g., locatedbeneath an outer surface of the NED 100).

Based on the one or more measurement signals generated by the one ormore position sensors 725, the IMU 730 generates fast calibration dataindicating an estimated position of the NED 100 relative to an initialposition of the NED 100. For example, the position sensors 725 includemultiple accelerometers to measure translational motion (forward/back,up/down, left/right) and multiple gyroscopes to measure rotationalmotion (e.g., pitch, yaw, roll). In some embodiments, the IMU 730rapidly samples the measurement signals from various position sensors725 and calculates the estimated position of the NED 100 from thesampled data. For example, the IMU 730 integrates the measurementsignals received from one or more accelerometers over time to estimate avelocity vector and integrates the velocity vector over time todetermine an estimated position of a reference point on the NED 100. Thereference point is a point that may be used to describe the position ofthe NED 100. While the reference point may generally be defined as apoint in space; however, in practice, the reference point is defined asa point within the NED 100.

The imaging device 735 generates slow calibration data in accordancewith calibration parameters received from the console 710. The imagingdevice 735 may include one or more cameras, one or more video cameras,any other device capable of capturing images, or some combinationthereof. Additionally, the imaging device 735 may include one or morefilters (e.g., used to increase signal to noise ratio). Slow calibrationdata is communicated from the imaging device 735 to the console 710, andthe imaging device 735 receives one or more calibration parameters fromthe console 710 to adjust one or more imaging parameters (e.g., focallength, focus, frame rate, ISO, sensor temperature, shutter speed,aperture, etc.).

The input/output interface 740 is a device that allows a user to sendaction requests to the console 710. An action request is a request toperform a particular action. For example, an action request may be tostart or end an application or to perform a particular action within theapplication. The input/output interface 740 may include one or moreinput devices. Example input devices include: a keyboard, a mouse, agame controller, or any other suitable device for receiving actionrequests and communicating the received action requests to the console710. An action request received by the input/output interface 740 iscommunicated to the console 710, which performs an action correspondingto the action request. In some embodiments, the input/output interface740 may provide haptic feedback to the user in accordance withinstructions received from the console 710. For example, haptic feedbackis provided when an action request is received, or the console 710communicates instructions to the input/output interface 740 causing theinput/output interface 740 to generate haptic feedback when the console710 performs an action.

The console 710 provides media to the NED 100 for presentation to theuser in accordance with information received from one or more of: theimaging device 735, the NED 100, and the input/output interface 740. Inthe example shown in FIG. 7, the console 710 includes an applicationstore 745, a tracking module 750, and a VR engine 755. Some embodimentsof the console 710 have different modules than those described inconjunction with FIG. 7. Similarly, the functions further describedbelow may be distributed among components of the console 710 in adifferent manner than is described here.

The application store 745 stores one or more applications for executionby the console 710. An application is a group of instructions, that whenexecuted by a processor, generates content for presentation to the user.Content generated by an application may be in response to inputsreceived from the user via movement of the NED 100 or the input/outputinterface device 740. Examples of applications include: gamingapplications, conferencing applications, video playback application, orother suitable applications.

The tracking module 750 calibrates the system 700 using one or morecalibration parameters and may adjust one or more calibration parametersto reduce error in determination of the position of the NED 100. Forexample, the tracking module 750 adjusts the focus of the imaging device735 to obtain a more accurate position for observed locators on thesystem 700. Moreover, calibration performed by the tracking module 750also accounts for information received from the IMU 730.

The tracking module 750 tracks movements of the NED 100 using slowcalibration information from the imaging device 735. The tracking module750 also determines positions of a reference point of the NED 100 usingposition information from the fast calibration information.Additionally, in some embodiments, the tracking module 750 may useportions of the fast calibration information, the slow calibrationinformation, or some combination thereof, to predict a future locationof the NED 100. The tracking module 750 provides the estimated orpredicted future position of the NED 100 to the VR engine 755.

The VR engine 755 executes applications within the system 700 andreceives position information, acceleration information, velocityinformation, predicted future positions, or some combination thereof ofthe NED 100 from the tracking module 750. In some embodiments, theinformation received by the VR engine 755 may be used for producing asignal (e.g., display instructions) to the waveguide display assembly715 that determines the type of content presented to the user. Forexample, if the received information indicates that the user has lookedto the left, the VR engine 755 generates content for the NED 100 thatmirrors the user's movement in a virtual environment by determining thetype of source and the waveguide that must operate in the waveguidedisplay assembly 715. For example, the VR engine 755 may produce adisplay instruction that would cause the waveguide display assembly 715to generate content with red, green, and blue color. Additionally, theVR engine 755 performs an action within an application executing on theconsole 710 in response to an action request received from theinput/output interface 740 and provides feedback to the user that theaction was performed. The provided feedback may be visual or audiblefeedback via the NED 100 or haptic feedback via the input/outputinterface 740.

Additional Configuration Information

The foregoing description of the embodiments of the disclosure has beenpresented for the purpose of illustration; it is not intended to beexhaustive or to limit the disclosure to the precise forms disclosed.Persons skilled in the relevant art can appreciate that manymodifications and variations are possible in light of the abovedisclosure.

Some portions of this description describe the embodiments of thedisclosure in terms of algorithms and symbolic representations ofoperations on information. These algorithmic descriptions andrepresentations are commonly used by those skilled in the dataprocessing arts to convey the substance of their work effectively toothers skilled in the art. These operations, while describedfunctionally, computationally, or logically, are understood to beimplemented by computer programs or equivalent electrical circuits,microcode, or the like. Furthermore, it has also proven convenient attimes, to refer to these arrangements of operations as modules, withoutloss of generality. The described operations and their associatedmodules may be embodied in software, firmware, hardware, or anycombinations thereof.

Any of the steps, operations, or processes described herein may beperformed or implemented with one or more hardware or software modules,alone or in combination with other devices. In one embodiment, asoftware module is implemented with a computer program productcomprising a computer-readable medium containing computer program code,which can be executed by a computer processor for performing any or allof the steps, operations, or processes described.

Embodiments of the disclosure may also relate to an apparatus forperforming the operations herein. This apparatus may be speciallyconstructed for the required purposes, and/or it may comprise ageneral-purpose computing device selectively activated or reconfiguredby a computer program stored in the computer. Such a computer programmay be stored in a non-transitory, tangible computer readable storagemedium, or any type of media suitable for storing electronicinstructions, which may be coupled to a computer system bus.Furthermore, any computing systems referred to in the specification mayinclude a single processor or may be architectures employing multipleprocessor designs for increased computing capability.

Embodiments of the disclosure may also relate to a product that isproduced by a computing process described herein. Such a product maycomprise information resulting from a computing process, where theinformation is stored on a non-transitory, tangible computer readablestorage medium and may include any embodiment of a computer programproduct or other data combination described herein.

Finally, the language used in the specification has been principallyselected for readability and instructional purposes, and it may not havebeen selected to delineate or circumscribe the inventive subject matter.It is therefore intended that the scope of the disclosure be limited notby this detailed description, but rather by any claims that issue on anapplication based hereon. Accordingly, the disclosure of the embodimentsis intended to be illustrative, but not limiting, of the scope of thedisclosure, which is set forth in the following claims.

What is claimed is:
 1. A waveguide display, comprising: a light sourceconfigured to emit image light in accordance with display instructions,the emitted image light propagates along an input wave vector; an outputwaveguide comprising: a waveguide body that includes a first surface anda second surface that is opposite to the first surface, a first gratingconfigured to receive the image light emitted from the light source andto couple the received image light into the waveguide body, a secondgrating included as part of the first surface of the waveguide body, anda third grating included as part of the second surface of the waveguidebody and positioned opposite to the second grating, at least one of thesecond grating and the third grating configured to output the imagelight to an eyebox, the output image light propagating along an outputwave vector that matches the input wave vector, wherein wave vectorsassociated with the first grating, the second grating, and the thirdgrating are of different magnitudes; and a controller configured togenerate the display instructions and provide the display instructionsto the light source.
 2. The waveguide display of claim 1, wherein thefirst grating is associated with a first wave vector, the second gratingis associated with a second wave vector, the third grating is associatedwith a third wave vector, and the vector sum of the first wave vector,the second wave vector and the third wave vector equal to zero.
 3. Thewaveguide display of claim 1, wherein the first grating includes a firstcoupling element on the first surface and a second coupling element onthe second surface.
 4. The waveguide display of claim 1, furthercomprising: a second output waveguide configured to receive the emittedimage light from the light source along a first dimension and to expandthe emitted image light along the first dimension.
 5. The waveguidedisplay of claim 1, wherein the light source is selected from a groupconsisting of: a laser diode, a vertical cavity surface emitting laser,a light emitting diode, a tunable laser, a MicroLED, a superluminous LED(SLED), and some combination thereof.
 6. The waveguide display of claim1, wherein each of the first grating, the second grating and the thirdgrating is selected from a group consisting of: a diffraction grating,and a holographic grating.
 7. The waveguide display of claim 1, whereinthe image light output from the output waveguide is monochromatic and ina first color band, and the waveguide display is part of a polychromaticdisplay that includes at least one other waveguide display that outputsimage light that is monochromatic and in a second color band that isdifferent than the first color band.
 8. An output waveguide comprising:a waveguide body that includes a first surface and a second surface thatis opposite to the first surface, a first grating configured to receiveimage light based on a plurality of light emitted from a plurality oflight sources and to couple the received image light into the waveguidebody, the emitted image light propagating along an input wave vector, asecond grating included as part of the first surface of the waveguidebody, and a third grating included as part of the second surface of thewaveguide body and positioned opposite to the second grating, at leastone of the second grating and the third grating configured to reflectthe image light at least twice and to output the image light to aneyebox, the output image light propagating along an output wave vectorthat matches the input wave vector.
 9. The output waveguide of claim 8,wherein the first grating is associated with a first wave vector, thesecond grating is associated with a second wave vector, the thirdgrating is associated with a third wave vector, and the vector sum ofthe first wave vector, the second wave vector and the third wave vectorequal to zero.
 10. The output waveguide of claim 8, wherein the firstgrating includes a first coupling element on the first surface and asecond coupling element on the second surface.
 11. The output waveguideof claim 8, wherein one of the light sources is selected from a groupconsisting of: a laser diode, a vertical cavity surface emitting laser,a light emitting diode, a tunable laser, a MicroLED, a superluminous LED(SLED), and some combination thereof.
 12. The output waveguide of claim8, wherein each of the first grating, the second grating and the thirdgrating is selected from a group consisting of: a diffraction grating,and a holographic grating.
 13. A near-eye display (NED), comprising: aframe; a waveguide display comprising: a plurality of light sourcesconfigured to emit image light in accordance with display instructions,the emitted image light propagates along an input wave vector; an outputwaveguide comprising: a waveguide body that includes a first surface anda second surface that is opposite to the first surface, a first gratingconfigured to receive the image light emitted from the light sources andto couple the received image light into the waveguide body, a secondgrating included as part of the first surface of the waveguide body, anda third grating included as part of the second surface of the waveguidebody and positioned opposite to the second grating, at least one of thesecond grating and the third grating configured to output the imagelight to an eyebox, the output image light propagating along an outputwave vector that matches the input wave vector, wherein wave vectorsassociated with the first grating, the second grating, and the thirdgrating are of different magnitudes; and a controller configured togenerate the display instructions and provide the display instructionsto the light sources.
 14. The near-eye display of claim 13, wherein thefirst grating is associated with a first wave vector, the second gratingis associated with a second wave vector, the third grating is associatedwith a third wave vector, and the vector sum of the first wave vector,the second wave vector and the third wave vector equal to zero.
 15. Thenear-eye display of claim of claim 13, wherein the first gratingincludes a first coupling element on the first surface and a secondcoupling element on the second surface.
 16. The near-eye display ofclaim 13, further comprising: a second output waveguide configured toreceive each of the emitted image light from each of the plurality oflight sources along a first dimension and expand the emitted image lightalong a second dimension orthogonal to the first dimension.
 17. Thenear-eye display of claim 13, wherein the image light is monochromaticand in a first color band, and the waveguide display includes at leastone other waveguide display that outputs image light that ismonochromatic and in a second color band that is different than thefirst color band.
 18. The near-eye display of claim 13, wherein each ofthe first grating, the second grating and the third grating is selectedfrom a group consisting of: a diffraction grating, and a holographicgrating.